The detection of drowsiness is of importance because drowsiness impairs the ability of operators of a wide range of equipment including motor vehicles, trains, aircraft and boats as well as industrial equipment. The problem of drowsy driving cannot be solved by educating drivers to take remedial action when feeling drowsy. The difficulty is that many people are unaware of their drowsiness at the time, even though they may be aware that they were drowsy after they rouse. This means one cannot predict when their level of drowsiness will next decrease to the point of danger because the drowsy state involves a loss of awareness of the present; an involuntary lapse of attention.
U.S. Pat. No. 5,745,038 discloses an eye monitor that examines reflected light from the eye to detect blinking behavior as an indicator of drowsiness.
U.S. Pat. No. 5,867,587 discloses a system which utilises digital images of the face and eyes of an operator, derives a parameter attributable to an eye blink and compares this to a threshold value of that parameter. A warning signal is given if the parameter falls below the threshold.
Patent specification WO 98/49028 also uses a video image as an eye gaze monitor to view a range of eye movements and analyse and compute a degree of alertness.
U.S. Pat. No. 6,091,334 discloses a system for analysing drowsiness which monitors head movement and gaze stability.
U.S. Pat. No. 6,102,870 uses eye tracker data such as fixations and saccades to infer mental states of the operator such as scanning, reading, searching, thinking and an intention to select. It is a system to enhance computer software responsiveness.
U.S. Pat. No. 6,097,295 discloses a system of image analysis based on eye pupil size.
U.S. Pat. No. 6,147,612 discloses a system of preventing sleep which detects eyelid movement and actuates an alarm when the eyelid movement is indicative of drowsiness.
U.S. Pat. No. 6,346,887 uses a video based eye tracking system which tracks eye activity and pupil diameter and position to produce a signal representing eye activity that can be used to estimate alertness.
WO 03/039358 disclosed an alertness monitor that used infra red light to measure the amplitude and velocity of eyelid and eye movements to derive a measure of alertness on a scale that can be related to the scale of blood alcohol levels. This monitor sought to provide a real time alertness monitor that can provide a calibrated measure of the operator's alertness.
It is an object of this invention to provide an improved alertness monitor of the type disclosed in WO 03/039358.